linux-kernel - Re: [PATCH 00/14] RFC: x86: relocatable kernel changes

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Message-ID: <4A047E53.8040003@intel.com>
Date:	Fri, 08 May 2009 11:47:47 -0700
From:	"H. Peter Anvin" <h.peter.anvin@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"hbabu@...ibm.com" <hbabu@...ibm.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"sam@...nborg.org" <sam@...nborg.org>
Subject: Re: [PATCH 00/14] RFC: x86: relocatable kernel changes

Eric W. Biederman wrote:
> 
> Perhaps we should have:
> init_size
> best start (As a 64bit field please)
> optimum align  (Or we flip it around)
> 

Thinking about this some more, I think you have a very good idea here.

Specifically, if we retcon the existing kernel_alignment field as 
"preferred alignment" (ignoring the naming issue for a bit), we can set 
that to 16 MB, which should give us correct behavior for all previously 
existing bootloaders.  Then we create a new "minimum alignment" field 
that newer bootloaders can use to relax the alignment requirement -- all 
the way down to 4K in the case of i386.  We document this field 
indicating that the bootloader should find the highest power of 2 <= 
preferred alignment, but down to this number.

The preferred address field becomes a readonly, advisory field; with it 
being readonly there aren't any funny issues with a strange loader 
writing a 64-bit address for a kernel which can't handle it (64-bit 
loading will still need substantial protocol changes, including how to 
find the entry point.)

Does that work for you?  That *should* address all your concerns, right?

	-hpa

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